Nuclear reactor having efficient and highly stable thermal transfer fluid

ABSTRACT

A pressurized water nuclear reactor (PWNR) includes a core having a containment shield surrounding a reactor vessel having fuel assemblies that contain fuel rods filled with fuel pellets, and control rods, and a steam generator thermally coupled to the reactor vessel. A flow loop includes the steam generator, a turbine, and a condenser, and a pump for circulating a water-based heat transfer fluid in the loop. The heat transfer fluid includes a plurality of nanoparticles having at least one carbon allotrope or related carbon material dispersed therein, such as diamond nanoparticles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a §371 national stage entry of InternationalApplication No. PCT/US2007/062582, filed Feb. 22, 2007, which claimspriority to U.S. Provisional Application No. 60/775,736, filed Feb. 22,2006, both of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to Pressurized Water Nuclear Reactors (PWNR)utilizing heat transfer fluids having nanoparticles dispersed thereinfor enhanced thermal transfer.

BACKGROUND

A pressurized water Nuclear reactor (PWNR) has a core immersed in waterin a large steel tank. The fuel rods and control rods make up a verticalarray. The control rods are movable, and are pulled up above the fuelrods when the plant is in full operation. The purpose of the controlrods is to absorb neutrons which trigger the splitting of atomic nucleiin the fissionable material in the fuel rods. With all the control rodsinserted, there is negligible fission (and heating) in the fuel rods.When the control rods are pulled out the fuel rods heat the water, whichis circulated by pumps in the primary or, inner loop, to a heatexchanger.

A feature of this design is that only the water in the inner loop is incontact with the radioactive fuel rods. Thus, only the inner loop hascontamination from the inevitable small amount of rust and corrosion.There are filters in this inner loop to capture the small particleswhich are radioactively contaminated. There are additional pumps tocirculate cooling water through the core, which form the Emergency CoreCooling System (ECCS). It is essential that circulation be maintained tocarry heat away from the fuel rods to prevent them from melting in theevent that the main primary circulation pumps should fail. The water inthe tank and the primary circulation loop is never supposed to boil, andthus always remain as water because steam is a much poorer conductor ofheat as compared to water. The fuel rods are supposed to always stayunder water. To prevent boiling, the tank and primary loop aremaintained at very high pressure.

The secondary loop water is heated through a heat exchanger with theprimary loop. Water in the secondary loop is allowed to boil in a steamgenerator tank. The steam is used to drive a turbine which turns anelectrical generator. The residual steam is condensed back to water,which is pumped back through the heat exchanger again to make moresteam. Also, circulation usually through a large cooling tower which isused to remove the waste heat.

One problem with conventional thermal transfer fluids used in PWNRs isthe onset of a heat transfer condition that can lead to a departure fromnuclei boiling (DNBR) that occurs at a condition call the critical heatflux. (CHF) which results in a blanketing of the fuel rod with bubblesthat interferes with heat transfer and leads to a condition calleddryout that can result in a critical failure of the fuel rods. What isneeded is nanofluid having enhanced thermal transfer and stability forPWNRs to raise the heat flux level at which dryout condition will occur.This heat flux level is called the critical heat flux (CHF).

SUMMARY

A pressurized water nuclear reactor comprises a core comprising acontainment shield surrounding a reactor vessel having fuel assembliesthat contain fuel rods filled with fuel pellets and control rods, and asteam generator thermally coupled to the reactor vessel. A flow loopcomprises the steam generator, a turbine, and a condenser, and a pumpfor circulating a water-based heat transfer fluid in the loop. The heattransfer fluid comprises a plurality of nanoparticles comprising atleast one carbon allotrope or related carbon material dispersed therein.As used herein, the phrase “carbon allotrope or related carbon material”includes the carbon allotropes, such as diamond, graphite, lonsdaleite,fullerenses including C60, C540 and C70, amorphous carbon and carbonnanotube, and related materials including pyrolitic carbon, carbon blackand diamond-like carbon. In some cases the allotrope or related materialis functionalized, such as hydoxy-functionalized fullerenes to promotedispersion in solution.

The diamond particles are typically primarily colloidal and have a meansize of 0.5 nm to 200 nanometers. In other embodiments of the inventionthe mean particle size is 1 nm to 100 nm, such as 40 nm to 100 nm. Aconcentration of nanoparticles can range from 0.0001 to 10 volumepercent of the heat transfer fluid, such as from 0.1 to 3 volume percentof the heat transfer fluid.

A method of transferring heat using a heat transfer fluid comprises thesteps of providing a water based heat transfer fluid comprising aplurality of carbon allotrope or related carbon material dispersedtherein, placing the heat transfer fluid in a system comprising acoolant loop including a heat source and a heat sink, and circulatingthe heat transfer fluid in the coolant loop during operation of thesystem. The system can comprise a pressurized water nuclear reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

A fuller understanding of the present invention and the features andbenefits thereof will be obtained upon review of the following drawings:

FIG. 1 shows the schematic of an exemplary pressurized water nuclearreactor that can be used with the present invention.

FIG. 2 shows particle size data for diamond particle samples dispersedin the simulated water chemistry under low boron conditions, shownbefore and after 24 hour autoclave at 275 C/2500 psi.

FIG. 3 shows particle size data for 1 wt % diamond (high boron content)in simulated BOC water. Before and after 24 hour autoclave at 275 C/2500psi.

FIG. 4 shows particle size data for 1 wt % diamond in low boron content)EOC water. Before and after 24 hour autoclave at 275 C/2500 psi.

FIGS. 5 and 6 show particle size data for 1 wt % diamond (high boroncontent) in water before and after 24 hour autoclave at 275 C/2500 psion the diamond powder at low boron (EOC) and high boron (BOC)concentrations, respectively.

FIG. 7 shows particle size data for 1 wt % diamond (high boron content)in water before and after a 500 hour run at EOC conditions, the datasuggesting that there may be some tendency to agglomerate at longerexposure periods.

FIG. 8 shows a typical BET straight line plot for as-received diamondpowder.

FIG. 9-11 show the as-received powder (dried but not rinsed), 24 hourlow boron autoclaved diamond, and the 500 hour low boron autoclaveddiamond, respectively.

DETAILED DESCRIPTION OF THE INVENTION

A pressurized water nuclear reactor (PWNR) 100 comprises a coreincluding a containment shield 105 surrounding a reactor vessel 110having fuel assemblies that contain fuel rods filled with fuel pellets115, and control rods 118, and a steam generator 120 thermally coupledto the reactor vessel 110. A flow loop includes the steam generator 120,a turbine 130, a condenser 135, and a pump 140 for circulating awater-based heat transfer fluid 145 in the loop. The heat transfer fluid145 comprises a plurality of carbon allotrope or related carbonnanoparticles, such as diamond nanoparticles, dispersed therein. Theturbine 130 is shown coupled to an electrical generator 150.

Carbon allotropes are the different molecular configurations(allotropes) that pure carbon can take. The eight known allotropes ofcarbon include diamond, graphite, lonsdaleite, C60, C540, C70, amorphouscarbon and carbon nanotube. Related essentially pure carbon relatedmaterials include pyrolitic carbon, carbon black, diamondoids(adamantames) and diamond-like carbon. The present Inventors have foundcarbon allotrope and related carbon materials provide low neutron crosssections, stability under typical pressures and temperatures present incore of PWNR reactors, chemical stability in the chemical environment ofa PWNR, and ability to remain dispersed in the heat transfer solutionunder typical pressure and temperature conditions.

The carbon allotrope or related carbon material are preferably colloidalnanoparticles having a mean size of 0.5 nm to 200 nm, and are generallyreferred to herein as nanoparticles for convenient reference. Theconcentration of nanoparticles generally ranges from 0.0001 to 10 volumepercent, such as 0.001, 0.01, 0.1, or 1%, of the total heat transferfluid. The nanoparticles can be natural or synthetic, such as syntheticdiamonds in the case of diamonds.

Although the Examples provided herein relate only to stability of heattransfer fluids according to the invention, tests carried out indicatethat inventive heat transfer fluids can defer the critical heat flux byup to about 50%. Thermal conductivity for heat transfer fluids accordingto the invention are also expected to be about 150% over conventionalPWNR water.

Other notable features regarding allotropic carbon or related carboncomprising nanoparticle comprising thermal transfer fluids according tothe invention include:

-   -   a.) Toleration of extreme environments:        -   i. Temperatures ranging from the solidification point of the            base fluid to the supercritical point of the base fluid;        -   ii. Pressures ranging from 1-10,000 psi;        -   iii. Flow rates ranging from 0-10 m/s; and        -   iv. Radioactive environment such as the core of a            Pressurized Water Nuclear Reactor.    -   b.) Both nanoparticle size and concentration can be low enough        to render the heat transfer fluid non-abrasive to the components        of the application, including but not limited to PWNR components        such as pumps, Zircaloys (a group of high-zirconium alloys),        stainless steel piping, etc. Non-abrasive, as used herein,        refers to no detection of erosion debris after 6 months (or        more) under simulated reactor conditions.    -   c.) The low neutron capture capability provided allows        application in the core of a PWNR which decreases the critical        heat flux (CHF) in a PWNR.

EXAMPLES

It should be understood that the examples described below are providedfor illustrative purposes only and do not in any way define the scope ofthe invention. For example, although the Examples all utilize diamondnanoparticles, as noted above the dispersed nanoparticles can be any ofthe carbon allotropes or related carbon materials.

The present Inventors determined that the extent to which nanoparticlesretain their size following exposure to PWNR autoclave conditions canprovide a measure of particle stability in a nuclear reactorenvironment. The effect of 24 hours under simulated PWNR conditions onparticle size was evaluated. Particle size distributions were firstcollected for all samples prior to the autoclave runs. The samples werethen taken to the autoclave, and were run at approximately 630° F. and2500 psi for 24 hours. The composition of the low boron samples for allexperiments described below was 1.6 ppm LiOH and 42.7 ppm boric acid.The composition of the high boron samples for all experiments describedbelow was 1.6 ppm LiOH and 1400 ppm boric acid.

A. Beckman-Coulter LS13320:

A Beckman-Coulter LS13320 laser diffraction size analyzer was used toinvestigate the effect of PWNR conditions on particle size distribution.The laser diffraction size analyzer utilizes a laser diffraction methodfor analyzing particle size distribution and measures particle sizesfrom 40 nm to 2,000 μm. Advantages of laser diffraction includesimplicity of operation, a built in mixer to keep particles dispersedand a broad dynamic size range encompassing the nano region from 40 nmup through 2 millimeters. Thus both primary particles and agglomeratescan be observed simultaneously giving an indication of the relativestate of agglomeration. FIG. 2 shows the volume distribution of the asreceived diamond particle samples dispersed in the simulated waterchemistry of beginning of cycle reactor fluid. Conditions were low boronconditions comprising 1.6 ppm LiOH and 42.7 ppm boric acid and a pH of6.9.

The volume plot shown in FIG. 2 indicates that only 20% of the diamondnanoparticles were well dispersed before autoclaving and this proportionappeared to increase slightly after PWNR conditions. There was also somegrowth in size of agglomerates in all runs. In both cases, the disperseddiamond fraction maintained a consistent size (number basis) in thevicinity of 75 nanometers (0.075 μm). The results were similar for thehigh boron (beginning of cycle shown in FIG. 3) water chemistry and forthe 500 hour low boron diamond run shown in FIG. 4.

B. Microtrac UPA 150

A Microtrac UPA 150 was used to better characterize particle sizedistributions in the nanometer range. The UPA 150 (Ultra-fine ParticleAnalyzer) is a dynamic light scattering method, and provides particlesize and the size distribution from approximately 0.003 μm to 6.54 μm.The Microtrac is designed to quantify nanoparticle dispersions only upto a few microns and therefore cannot detect the fraction of largeagglomerated material, which settles rapidly out of the detection volumein the unstirred 20 ml sample cell. Thus it provides a goodrepresentation of the dispersed fraction of material.

FIGS. 5 and 6 represent UPA 150 volume distributions for 1 wt % diamond(high boron content) in water after =24 hour autoclave at 275 C/2500 psion the diamond powder at low boron (EOC) and high boron (BOC)concentrations, respectively. The results are consistent with the laserdiffraction data and show a low tendency towards agglomeration. FIG. 7shows UPA 150 volume distributions for 1 wt % diamond (high boroncontent) in water before and after a 500 hour run at EOC conditionswhich suggests that there may be some tendency to agglomerate at longerexposure periods. However, the reactor used for the tests was a staticreactor with no stirring or circulation to promote dispersionagglomeration. Accordingly, agglomeration can likely be significantlyreduced by including the reactor with a means for stirring orcirculation to promote dispersion.

C. BET Surface Area:

A Brunauer-Emmett-Teller (BET) surface area analyzer estimates thespecific external surface of a solid by determining the volume of aspecific gas that is absorbed under controlled conditions. BET surfacearea was measured using a Quantachrome NOVA 1200 Surface Area Analyzerto analyze any changes in specific surface area in diamond due to 24hours at PWNR conditions. This instrument performs rapid and accuratesorption measurements of nitrogen gas on particle surfaces to directlymeasure surface area. Prior to gas adsorption, the powder sample wasdegassed and dried in a vacuum at a temperature of 180° C. Measurementsmade by this instrument include multipoint BET method surface area,single point BET surface area, 25 point adsorption isotherms, 25 pointdesorption isotherms, total pore volume, average pore radius, and BJHpore size distribution based on the adsorption or desorption isotherm.FIG. 8 shows a typical BET straight line plot for as-received diamondpowder. Table 1 (below) shows BET data for the 24 hour autoclave runsand the single 500 hour autoclave run on the diamond sample. BET surfacearea measurements are normally reproducible to within 5%. The data intable one indicates some degradation of surface area after autoclavingwith the largest decrease (˜15%) observed for the 500 hour run. Theformula for calculating the geometric diameter of a sphere from thespecific surface area is:

$d_{microns} = \frac{6}{{\rho\left( {g\text{/}{cm}^{3}} \right)} \times {S.S.A.\left( {m^{2}\text{/}g} \right)}}$where d is the diameter in microns, ρ is the density in g/cm³ and S.S.A.For the diamond, the as-received surface area of 97.7 m²/g, equates to aspherical equivalent diameter of 17.8 nanometers (ρ=3.45) which is farsmaller than the measured mean particle size. This discrepancy isconsistent with the large relatively hard agglomerates which are made upof the primary nanoparticles. These provide microporous interparticlespacing in which the nitrogen can condensed during analysis. Inaddition, the manufacturer has indicated that the particles areengineered with surface features (microcracks) that may enhance nitrogenadsorption. The bulk of the decrease in surface area for the 500 hourruns is likely to occur inside these diamond agglomerates.

TABLE 1 BET surface area for diamond runs. BET Sample ID Surface areaCorrelation As Received Diamond 105.5 .9980 As Received Diamond 90.1.9998 44 (high boron) Before autoclaving (as 105.8 .9998 received) 38(low boron) After autoclaving 24 hrs 98.28 .9990 39 (low boron) Afterautoclaving 24 hrs 103.0 .9953 40 (low boron) After autoclaving 24 hrs87.5 .9999 41 (low boron) After autoclaving 500 hrs 85.8 .9991 44 (highboron) After autoclaving 24 hrs 104.4 .9998D. Zeta Potential Brookhaven Instruments

The zeta potential of the nanoparticulates was measured by theelectrophoretic mobility method using photon correlation spectroscopy.For most ensemble size measurements techniques what is really measuredis the agglomerate size distribution. Thus, the size distribution ishighly dependent on the state of dispersion of the system. Any ensembleparticle size measurement must be interpreted in this context. Due toattractive forces (Van der Waals, and other), particles will tend toagglomerate in suspension unless stabilized by surface charge or stericeffects. Most aqueous suspensions of hydrophilic powders willspecifically adsorb or desorb hydrogen ions to generate a surfacecharge. Homogeneous powders that develop a surface charge high enough toovercome interparticle attraction will form more stable dispersions. Thepoint of zero charge is approximated by measuring the isoelectricpoint—that is, the pH at which the zeta potential is zero. The pH atwhich this occurs is material dependent. For a native diamond oxidesurface the isoelectric point tends to be low. The charge is morepositive as the pH (acidic solutions) decrease below the isoelectricpoint and more negative as the pH rises above the IEP. The closer the pHis to the isoelectric point the greater the tendency for the material toagglomerate. Table 2 shows the zeta potential for the diamond bothbefore and after autoclave treatment. In general the diamond displays arelatively high negative zeta potential under all conditions tested. Thezeta potential was significantly lower in the high boron containingsample (BOC) to the higher ionic strength of the solution (10 timesgreater than EOC samples). This is expected, as high ionic strengthtends to suppress the double layer and reduce the zeta potential. Thezeta potential was the highest for the 500 hour autoclave (EOCconditions) run. This bodes well for the stability of diamond nanopowderdispersions under these conditions.

TABLE 2 Zeta potential measurements for diamond runs before and afterautoclaving. Zeta Potential Standard Sample (mV) Error pH  24 hour LowBoron (before) −34.11 0.82 6.7-6.8  24 hour Low Boron (after) −28.9 0.876.75  24 hour High Boron #44 (before) −16.16/−24.9 1.05/ 6.82  24 hourHigh Boron #44 (after) −20.8 1.75 6.82 500 hour Low Boron #41(before)−28.85 0.92 6.73 500 hour Low Boron #41(after) −26.25 0.83 6.76 500 hourLow Boron #41(after) −39.5 1.09 6.8E. JEOL 3035 Field Emission SEM and JEOL-2010F Scanning TEM:

Diamond surface morphology was examined using both SEM and TEM. Scanningelectron microscopy revealed very large particles appearing to befractured bulk material. Further testing, discussions with themanufacturer and TEM indicated that these particles actually were hardporous agglomerates of the about 75 nm average primary particles. Thefracture surfaces most likely are the results of the manufacturergrinding the pan dried nanomaterial for packaging. These agglomerateswere impossible to redisperse in their entirety. High energy sonicationproduced an average of 20% dispersion (by mass) into the desired nanoparticle size. The remaining 80% stayed agglomerated even throughsimulated PWNR conditions.

TEM analysis was performed on the nanodispersed phase. Scanned imagestaken with TEM for a sample of diamond not exposed and after exposure toPWNR conditions. The diamond morphology did not appear to besignificantly affected by exposure to PWNR conditions.

F. X-Ray Diffraction (XRD):

X-ray diffraction measurements were conducted on powders before andafter autoclaving at PWNR conditions to determine if any changes couldbe observed in crystal structure. For the diamond, no changes were notedbetween the as received and post treatment samples. FIGS. 9-11 show theas-received powder (dried but not rinsed), and the 500 hour low boronautoclaved diamond, respectively. The powders were dried and analyzeddirectly from the reactor water without rinsing to avoid loss ofpotential nanoparticulate phases. Consequently, crystallized soluble(lithium borate hydrates) species are apparent in spectra, particularlythe high boron (BOC) samples. No graphitic peaks (2θ=26.53/100,44.63/50, 54.70/80) or other carbon phases were observed.

G. FTIR and RAMAN Spectroscopy:

In addition, the three diamond samples were analyzed with FTIR and withRAMAN spectroscopy. These instruments can be used to identifydifferences in the functional groups present on the surface and in thebulk for many materials including gases, liquids, solids, fibers, andthin films.

RAMAN was used to observe changes in the surface chemistry of thematerial during the autoclave run. Micro-RAMAN spectra obtainedevidenced how little the Raman spectra changes during the low boronautoclave run. The RAMAN intensities are quite low, and the peaks arenot sharp. However, there appears to be little change after exposure toPWNR conditions. These are typical results for the low boron runs. RAMANwas not performed on the high boron or 500 hour runs.

The FTIR spectra of these powders gives a better indication of thesurface composition of the nano diamond powders. A diffuse reflectancesampling apparatus (Gemini, Spectra Tech) was used to maximize theamount of surface information. The spectra of the initial powder andthat of the three low boron replicates prior to autoclaving wereobtained. (Thus the powder was suspended, then dried at about 100degrees Celsius for about 1 h. It was diluted with dry potassium bromideat about 1 weight percent prior to analysis.) These powders allexhibited peaks in the 3700-2700 cm⁻¹ range typically associated withhydroxyl bonds. There is a strong peak at about 1720 cm⁻¹ which (alongwith others) indicates the presence of carboxylic acid groups. The peakat about 1615 cm⁻¹ is probably due to aromatic carbon-carbon doublebonds. In short, the features shown are typical of a partially oxidizedcarbon surface.

The FTIR spectra for the nanodiamond powder do show some minordifferences after exposure to PWNR conditions. The IR spectra of thenanodiamond powder (EOC) dried from solution both before and afterexposure in the autoclave revealed several differences. The hydroxylpeak (about 3000-3700 cm⁻¹) is slightly reduced in intensity and the CHstretching peaks around 2800-3000 cm⁻¹ increase in intensity. Smallpeaks at about 1520 and 760 cm⁻¹ also form.

The results disclosed above indicate that the diamond comprising thermaltransfer system provides a high level of dispersion stability. Chemicalstability of the diamond appears excellent, although higher qualitydiamond nanopowders may provide even better results. All nanopowders arepreferably obtained in an aqueous dispersed state when possible. Thedispersion stability of diamond also appears quite good.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description as well as the examples which follow are intendedto illustrate and not limit the scope of the invention. Other aspects,advantages and modifications within the scope of the invention will beapparent to those skilled in the art to which the invention pertains.

The invention claimed is:
 1. A pressurized water nuclear reactor,comprising: a core comprising a containment shield surrounding a reactorvessel having fuel assemblies that contain control rods and fuel rodsfilled with fuel pellets, and a steam generator thermally coupled tosaid reactor vessel via a primary flow loop; a secondary flow loopcomprising said steam generator, a turbine, a condenser, and a pump forcirculating a water-based heat transfer fluid in said secondary flowloop, wherein said heat transfer fluid comprises a plurality ofnanoparticles comprising at least one carbon allotrope or related carbonmaterial dispersed therein.
 2. The pressurized water nuclear reactor ofclaim 1, wherein said at least one carbon allotrope or related carbonmaterial comprises diamond nanoparticles.
 3. The pressurized waternuclear reactor of claim 2, wherein said diamond nanoparticles areprimarily colloidal.
 4. The pressurized water nuclear reactor of claim2, wherein said diamond nanoparticles have a mean size that is in arange from 0.5 nm to 200 nanometers.
 5. The pressurized water nuclearreactor of claim 4, wherein said mean size is in a range from 1 nm to100 nm.
 6. The pressurized water nuclear reactor of claim 4, whereinsaid mean size of said plurality of nanoparticles is in a range from 40nm to 100 nm.
 7. The pressurized water nuclear reactor of claim 1,wherein said at least one carbon allotrope or related carbon materialcomprises fullerenes.
 8. The pressurized water nuclear reactor of claim1, wherein said at least one carbon allotrope or related carbon materialcomprises carbon nanotubes.
 9. The pressurized water nuclear reactor ofclaim 1, wherein a concentration of said plurality of nanoparticles insaid heat transfer fluid is in a range from 0.0001 to 10 volume percentof said heat transfer fluid.
 10. The pressurized water nuclear reactorof claim 9, wherein said concentration of said plurality ofnanoparticles in said heat transfer fluid is in a range from 0.1 to 3volume percent of said heat transfer fluid.